Ultrasound-induced cracking and pyrolysis of some aromatic and naphthenic hydrocarbons

The action of intense ultrasound on solutions of decahydronaphthalene (decalin) or tetrahydronaphthalene (tetralin) causes, in both cases, a dehydrogenation reaction at room temperature. According to thermodynamic calculations, temperatures as high as 500 degrees C are necessary to achieve the same results. The use of Pd and Se as dehydrogenation catalysts has confirmed the dehydrogenation reactions. Benzene and toluene sonication at room temperature causes aromatic ring breakdown with formation of acetylene and other products. The analogy with radiolysis was noticed. A thermodynamic analysis was conducted on the possible reaction products formed from benzene ring cleavage including polymerization products. It was concluded that acetylene formation from benzene is possible for instance at 650 degrees C only if it is accompanied by coke formation. Otherwise temperatures as high as 1700 degrees C are needed. The nature of the 'coke' formed during sonication is discussed, it was revealed by FT-IR spectroscopy to be a crosslinked polystyrene and hence it is a sonopolymer derived from benzene or toluene ring breakdown products reacted with phenyl and polyphenyl radicals. Again the striking analogy between the IR spectrum of irradiated polystyrene and benzene sonopolymer was noticed. The formation of poly-p-phenylene was excluded by the FT-IR pattern which did not match that of an authentic sample. (C) 2000 Elsevier Science B.V. All rights reserved.